problem with urlencode and ampersand

[debk]

Server.UrlEncode is not longer converting the ampersand in a string to
%26 so the value passed in the querystring gets truncated in the
following page. Is this a problem with IIS, does anyone know? I can't
find this reported anywhere else. I may just have to code around it.
Details:
link is created by the following code:
<a>href="GroupDetails.asp?groupName=<%=Server.URLE ncode(objRecordset("Group_Name"))%>">Group
Details</a>

If Group_Name contains an ampersand, this appears as & in the
querystring instead of being converted by URLEncode to %26. When the
groupName querystring value is used in the new page, it is truncated.
So "A & M AllStars" is truncated to "A".

However, this only occurs in 1 environment, in our dev environment it
works fine and converts ampersand so it doesn't muck up the
querystring. I can't find any obvious setting in IIS which would
affect this, but presumably it must be happening on the server and is
nothing to do with browser, browser version etc. I assume a security
patch has caused this. Any help would be appreciated.